Third Generation Partnership Project (3GPP) considers that the deployment of small cells (cells which are established by low-power base stations, and the small cells are distinguished from macro cells established by macro base stations) and enhancement of capabilities of the small cells are one of subjects which are most interested by people in future development of communication networks. At present, a heterogeneous network deployment scenario commonly approved by the communication industry is that low-power nodes are deployed in a coverage range of a macro base station or at a boundary of the macro base station, and the macro base station and the low-power nodes jointly form a Radio Access Network (RAN) in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) system, to provide combined data transmission services for User Equipment (UE).
For a system architecture under the typical scenario, an example illustrated in FIG. 1 may be referred. In the RAN, a base station which has an S1-MME interface with a Mobility Management Entity (MME) in a Core Network (CN) and is considered as a mobile anchor point by the CN is called a Master eNB (MeNB). A node which is connected with MeNB through an X2 interface and provides additional radio resources for UE is called a Secondary eNB (SeNB). Radio Uu interfaces are established between UE and MeNB and between UE and SeNB, and control plane signaling and user plane data may be transmitted on the interfaces, which is also called that UE is in a Dural Connectivity (DC) state. Since the system architecture allows two (even more) base stations to simultaneously provide radio resources for one UE to support communication services, data throughput of the network is greatly improved and can satisfy increasing demands of users for data rate as possible.
For a user plane transmission mode and a form of a protocol stack under the system architecture, two examples illustrated in FIG. 2a and FIG. 2b may be referred. By taking downlink data as an example, a transmission mode of an Evolved Packet System (EPS) bearer #1 is the same as a standard mode of a single connectivity system, i.e., a Serving Gateway (S-GW) sends data packets to an MeNB through an S1-U interface, and then the MeNB sends the data packets to UE through a Uu interface. In DC, a bearer having a radio protocol stack only located at MeNB and only using MeNB resources is called a Master Cell Group (MCG) bearer. As illustrated in FIG. 2a, this mode is temporarily called user plane architecture mode 1 in this document. A transmission of an EPS bearer #2 is that data packets are sent to an SeNB through an S1-U interface directly connected to SeNB, and then the SeNB sends the data packets to UE through a Uu interface; and a bearer having a radio protocol stack only located at SeNB and only using SeNB resources is called a Secondary Cell Group (SCG) bearer. As illustrated in FIG. 2b, this mode is temporarily called user plane architecture mode 2 in this document. A transmission of EPS bearer #2 is that S-GW sends data packets to the MeNB through an S1-U interface, then the MeNB only sends one part of data packets of the bearer to UE through a Uu interface, and the other part of data packets are delivered to SeNB through an X2 interface and then the SeNB sends this part of data packets to UE through a Uu interface; and a bearer having radio protocol stacks located at MeNB and SeNB and using MeNB and SeNB resources to transmit is called a split bearer. In this document, the SCG bearer and the split bearer are collectively called split bearers.
In a process that UE transmits data and/or moves, there are two scenarios. One scenario is that, for example, when a variable in a protocol entity is accumulated to a certain threshold, partial configuration parameters of the UE need to be modified. The other scenario is that, for example, when a radio signal quality decreases to a certain threshold or the load of a current serving base station is too heavy, the serving base station of the UE needs to be handed over from a current connected eNB (called source eNB) to another eNB which satisfies conditions (called a target eNB). The two scenarios need to be realized through a procedure of intra-eNB handover (UE still establishes a connection with the same eNB before and after handover and only partial parameters are reconfigured) or inter-eNB handover (UE establishes connections with different eNBs before and after handover).
Under the system architecture in this document, when MeNB of UE in a DC state needs to be handed over, according to the related art, the SeNB of UE will be released before or after a handover procedure. If there are service demands or base station nodes which have suitable conditions after the UE accesses the target eNB (for the intra-eNB handover, the target eNB is the source MeNB), the target eNB will add an SeNB for the UE again. In an exemplary embodiment, for the intra-eNB handover, if the conditions of the source SeNB always satisfy a specific threshold, the MeNB may simultaneously carry (intra-) handover information of the MeNB and release and addition information of the SeNB in one piece of control plane signaling, i.e., the UE is indicated to perform reconfiguration on resources of the two eNBs through this piece of signaling only.
Accordingly, it can be seen that, under the network design capability in the related art, a link between the UE and the SeNB will be interrupted due to MeNB handover of UE, and the protocol entity related to the split bearer also needs to be reestablished. Even though in a preferred intra-MeNB handover procedure, if time spent by UE in accessing a cell of the target eNB is relatively long, time of interruption of user plane data between the UE and the SeNB will also be lengthened accordingly. That means that radio resources which can be provided by the network for UE are non-occupied, i.e., data throughput of UE which originally can be improved is limited for this reason, and thereby the overall service performance of the network is decreased.